The present invention relates to novel processes for separation of fluid mixtures. Broadly, intergrated processes of the invention comprise a plurality of separations using solid perm-selective membranes. More particularly, the invention relates to recovery of specified products using a plurality of membrane modules disposed in a first product group, a second product group, and optionally one or more intermediate group. Processes of the invention with the membrane modules in multiple groups are beneficially useful for simultaneous recovery of a very pure permeate product and a desired non-permeate product from a mixture containing organic compounds.
Light hydrocarbons serve as the building blocks for the production of numerous chemicals. Ethylene, a light olefin composed of two carbon atoms joined by a double bond, is used in the production of several chemicals including polyethylene, ethylene oxide, ethylene dichloride, and ethylbenzene. Propylene, a light olefin composed of three carbon atoms where two of the carbon atoms are joined by a double bond, is used in the manufacture of polypropylene, acrylonitrile, oxo alcohols, cumene, and propylene oxide. Light hydrocarbons composed of four carbon atoms are used, for example, in the production of synthetic rubbers and elastomers, sec-butyl alcohols, maleic anhydrides, polybutenes, and clean motor fuels (e.g. alkylate).
These light hydrocarbons have traditionally been produced by steam or catalytic cracking. Oxygenate conversion (e.g. methanol to olefins), dehydrogenation, and isomerization routes have also grown in recent years as important production routes. Separation costs are a significant fraction of the overall costs of making these petrochemicals. When the valuable light hydrocarbons are produced, they are often accompanied by the production of other compounds that must be removed. For example, when propylene is produced in the presence of hydrogen, it is often produced in conjunction with propane. Generally, it is required to remove the propane before propylene can be used to produce more valuable products. However, many of the desirable light hydrocarbons are produced with compounds that have boiling points that are very similar to those of the desirable light hydrocarbons. These separations then become very expensive and energy intensive. For example, a typical ethylene separation section of an ethylene plant requires cryogenic conditions to achieve the required ethylene purity. A propane/propylene splitter requires so many separation stages that it is typically done in two large towers each containing more than 100 trays.
Processes that enable the concentration and recovery of these desirable light hydrocarbons without expensive distillation steps have been sought for many years.
In U.S. Pat. No. 3,758,603 and 3,864,418 R. Hughes and E. Steigelmann describe the use of membranes in conjunction with metal complexing techniques to facilitate the separation of ethylene from ethane and methane. Similar metal complex and membrane hybrid processes have been described by R. Yahnke in U.S. Pat. No. 4,060,566, by M. Kraus in U.S. Pat. No. 4,614,524, and by R. Valus in U.S. Pat. No. 5,057,641. These processes utilize a separation unit containing a membrane having a feed side and a permeate side with a liquid between them that contains a metal-containing ion complexing agent. Transport of the desired component is described as occurring by a) dissolving the component in the facilitator liquid on the feed side of the membrane; b) forming a component-carrier complex; c) diffusing the complex to the permeate side of the membrane; and d) releasing the component from the carrier. The selectivity of the membrane is maximized by choosing a complexing agent with a high affinity for the desired component. The agent facilitates the transport of the desired component from the feed stream to the permeate.
Evaluation of a facilitated transport membrane process for the separation of propylene from propane is described by J. Davis et al. in an article entitled xe2x80x9cFacilitated Transport Membrane Hybrid Systems for Olefin Purificationxe2x80x9d published in Sep. Sci. Tech 28, 463-476 (1993). Davis et al. used a silver nitrate solution in a hybrid membrane system to obtain selectivities for propylene transport that were in excess of 150.
D. Gottschlich and D. Roberts examined hybrid systems consisting of a distillation column and a facilitated transport membrane separation module in paper for SRI Project 6519 and DOE Contract Number DE-AC07-761D01570 entitled xe2x80x9cEnergy Minimization of Separation Process Using Conventional/Membrane Systemsxe2x80x9d (1990). They compare the effectiveness of several arrangements of facilitated transport membranes and distillation processes.
R. Noble and co-workers in two articles entitled xe2x80x9cAnalysis of a Membrane/Distillation Column Hybrid Processxe2x80x9d published in J. Memb. Sci. 93, 31-44 (1994) and xe2x80x9cDesign Methodology for a Membrane/Distillation Column Hybrid Processxe2x80x9d published in J. Memb. Sci.99, 259-272 (1995) discuss the design and optimization of several combined membrane and distillation processes for the separation of propylene and propane. Their work focuses on the placement of the membrane around the distillation column in order to obtain an efficient process that accomplishes the desired separation.
Friesen et al. describe the use of a membrane system to separate propylene from propane in European Patent Application 0701856A1 where the flux of propylene through the membrane has been enhanced by the use of a condensable sweep gas on the permeate side of the membrane. They present examples for a membrane that illustrate the effect of sweep gas rate on propylene flux.
Handbooks and review articles on membrane separation processes extol the simplicity and efficiency of membranes. However, the prior art for using membranes to separate desirable hydrocarbons (e.g. olefins) out of complex mixtures only considers the use of membranes in hybrid systems, where membranes have been combined with facilitating liquids or distillation columns. These other separation processes have inherent difficulties that could undermine their coupling with membranes. For example, the metal complexing agents described above are often very susceptible to poisoning. A. Sungpet et al. state in an article entitled xe2x80x9cSeparation of Ethylene from Ethane Using Perfluorosulfonic Acid Ion-Exchange Membranesxe2x80x9d published in ACS Symposium Series xe2x80x9cChemical Separations with Liquid Membranes,xe2x80x9d 270-285 (1996) that the selectivity and permeability of membranes for the separation of hydrocarbon mixtures, such as olefins from paraffins, is too low to be attractive, so membranes have been combined with other separation processes to achieve the desired separation. However if a membrane material was developed with sufficient permeability and selectivity where it could be used without other separation steps, it is not clear how to utilize the material in an industrial process. Detailed designs and evaluations of processes where the separation of desirable hydrocarbons is accomplished only by membranes are lacking. An understanding of the effect of membrane selectivity and process configuration on the energy and amount of membrane area required to separate desirable hydrocarbons out of complex mixtures is needed.
There is a present need for processes and apparatus using perm-selective membranes for simultaneous recovery of a very pure permeate product and a desired non-permeate product, in contrast to by-product, waste streams, in particular, processes which do not have the above disadvantages. A further object of the invention is to provide inexpensive processes and apparatus for the efficient separation of chemical compounds from mixtures which are difficult to separate, e.g., separation of propane-propylene by fractional distillation.
Improved processes should provide for an integrated sequence, carried out with streams in gas and/or liquid state, using a suitable perm-selective membranes, preferably a solid perm-selective membrane which under a suitable differential of a driving force exhibits selective permeability of a desired product. Advantageously, processes using perm-selective membranes for simultaneous recovery of a very pure permeate product and a desired non-permeate product shall avoid or minimize formation of unwanted by-products, waste streams. Beneficially, an improved separation processes shall efficiently employ perm-selective membranes having the same or different pre-selected permeabilities, and with optimum distribution between stages so as to efficiently produce very high purity product.
Economical processes of the present invention are for separation of fluid mixtures to recover desired products with apparatus using solid perm-selective membranes. More particularly, this invention relates processes using apparatus comprising a plurality of membrane modules disposed in a first product group, a second product group, and optionally one or more intermediate group. Advantageously intergrated processes of the invention with the membrane modules in multiple groups are employed for simultaneous recovery of a very pure permeate product and a desired non-permeate product from a mixture containing organic compounds.
This invention contemplates the treatment of a fluid feedstock, e.g. various type organic materials, especially a fluid mixture of compounds of petroleum origin. In general, the fluid feedstock is a gaseous mixture comprising a more selectively permeable component and a less permeable component. Processes of the invention are particularly useful in processes for treatment of a gaseous mixture comprised of a more selectively permeable alkene component and a corresponding alkane component.
Advantageously, processes according to the invention treat feedstreams which comprises a mixture of an alkane compound having from 2 to about 4 carbon atoms and an alkene compound having the same number of carbon atoms as the predominate component of the feedstream, e.g. the separation of propylene from propane.
In one aspect, the invention provides a process using perm-selective membranes in multiple groups for simultaneous recovery of a permeate product and a desired non-permeate product from a fluid mixture of compounds. The process comprises: providing a feedstream comprising a mixture of two or more compounds, providing apparatus comprising a plurality of membrane modules each including first and second zones separated by a solid perm-selective membrane which under a suitable differential of a driving force exhibits a permeability of at least 0.1 Barrer for one of the compounds of the feedstock, each first zone having at least one inlet and outlet for flow of fluid in contact with the membrane, and contiguous with the opposite side thereof a second zone having at least one outlet for flow of permeate, and the membrane modules of the apparatus are disposed in a first product group, a second product group, and at least one intermediate group, which intermediate group has membranes of higher selectivity than the membranes in at least one of the other groups, introducing the feedstream into the first zone of one or more of the intermediate modules under conditions suitable for permeation, and thereby obtaining permeate effluents and non-permeate streams from the intermediate modules, distributing the non-permeate streams from the intermediate modules into the first zone of one or more of the second product modules under conditions suitable for permeation, second product, collecting the permeate effluents from the second zones of the intermediate group of modules and distributing the permeates into the first zones of the first product group modules under conditions suitable for permeation, thereby obtaining non-permeate streams and final permeate product streams from the first product modules, and distributing the non-permeate streams from the first product modules into the first zone of one or more of the intermediate modules under conditions suitable for permeation.
Processes of the invention advantageously further comprises: collecting the permeate effluents from the second zones of the second product modules and distributing the permeates into the first zones of the first product group modules. In other aspects processes according to the invention further comprises: collecting the permeate effluents from the second zones of the second product modules and distributing the permeates into the first zones of the intermediate group of modules.
The means for collection and distribution of permeate effluents and permeate streams, advantageously comprises a compressor and/or a pump, preferably a compressor. Optionally, the apparatus may further comprises means for distribution of a xe2x80x9csweepxe2x80x9d stream into the second zones one or more of the modules to improve recovery of the permeate effluents.
In another aspect, this invention provides a process using perm-selective membranes in multiple groups for simultaneous recovery of a permeate product and a desired non-permeate product from a fluid mixture of compounds, which process comprises: providing a feedstream comprising a mixture of two or more organic compounds, providing apparatus comprising a plurality of membrane modules disposed in a first product group, one or more intermediate group, and a second product group, each module comprising first and second zones separated by a solid perm-selective membrane which under a suitable differential of a driving force exhibits a permeability of at least 0.1 Barrer for one of the compounds of the feedstock, each first zone having at least one inlet and outlet for flow of fluid in contact with the membrane, and contiguous with the opposite side thereof a second zone having at least one outlet for flow of permeate, introducing the feedstream into the first zone of one or more of the intermediate modules under conditions suitable for permeation, and thereby obtaining permeate effluents and non-permeate streams from the intermediate modules, collecting the permeate effluents from the second zones of one or more of the intermediate group modules, and distributing the permeates into the first zones of the first product group modules, under conditions suitable for permeation, and thereby separating therefrom non-permeate effluents and final permeate product streams, distributing the non-permeate streams from one or more of the intermediate modules into the first zone of the second product modules under conditions suitable for permeation, and thereby obtaining permeate effluents and non-permeate second product streams from the second product modules, collecting the permeate effluents from the second zones of the second product modules, and distributing the permeates into the first zones of the first product group of modules, and distributing the non-permeate streams from the first product modules into the first zone of one or more of the intermediate modules.
Processes of the invention are particularly useful for treatment of a gaseous mixture comprised of a more selectively permeable alkene component and a corresponding alkane component, e.g. the feedstream comprises a mixture of an alkane compound having from 2 to about 4 carbon atoms and an alkene compound having the same number of carbon atoms as the predominate component of the feedstream. Generally, the mixtures have a liquid volume ratio of the alkene to the alkane compounds in a range upward from about 1 about 9. Advantageously, this ratio is in a range from about 1.25 to 8. Where the feedstream comprises a mixture of propylene and propane the liquid volume ratio of propylene to propane is in a range upward from about 1.5 to about 4, and more preferably the ratio is in a range from about 2 to about 3.
Typically, processes of the invention provide a first product of a more selectively permeable component and a corresponding less selectively permeable component having a liquid volume ratio of the more selectively permeable component to the less selectively permeable component in a range upward from about 10. Where the first product comprises a mixture of propylene and propane the liquid volume ratio of propylene to propane is in a range upward from about 14, and more preferably the ratio is at least 19.
According to the invention, the membrane modules in a group having membranes of about the same selectivity which selectivity is about the same, or may be critically different from that of the other group or groups. In one aspect of the invention the membrane modules in the second product group have membranes of lower selectivity than membranes in at least one of other group. Preferably, the membrane modules in the second product group have membranes of lower selectivity than membranes in the other groups.
In another aspect of the invention the membrane modules in at least a portion of the intermediate group have membranes of higher selectivity than membranes in at least one of the other groups. Advantageously, the membrane modules in the intermediate group have membranes of a selectivity which is about 35 percent or more higher than membranes another group, preferably at least about 50 percent higher, and more preferably at least about 100 percent higher. Preferably, the membrane modules in at least a portion of the intermediate group have membranes of higher selectivity than membranes in the other groups.
In other preferred embodiments, the membrane modules in the first product group have membranes of higher selectivity than membranes in at least one of the other groups. More preferably the membrane modules in the first product group have membranes of higher selectivity than membranes in the other groups.
This invention is particularly useful towards separations involving organic compounds, in particular compounds which are difficult to separate by conventional means such as fractional distillation. Typically, these include organic compounds are chemically related as for example alkanes and alkenes of similar carbon number.
According to the invention, under conditions suitable for permeation, the fluid in contact with the membranes in one or more of the module groups is liquid, gas, or a combination thereof.
In another aspect, this invention provides a process using perm-selective membranes in multiple groups for simultaneous recovery of a permeate product and a desired non-permeate product from a fluid mixture of compounds, which process comprises: providing a feedstream comprising a mixture of two or more organic compounds, providing apparatus comprising a plurality of membrane modules each including first and second zones separated by a solid perm-selective membrane which under a suitable differential of a driving force exhibits a permeability of at least 0.1 Barrer for one of the compounds of the feedstock, each first zone having at least one inlet and outlet for flow of fluid in contact with the membrane, and contiguous with the opposite side thereof a second zone having at least one outlet for flow of permeate, and the membrane modules of the apparatus are disposed in a first product group, a second product group, and at least one intermediate group, which intermediate group has membranes of higher selectivity than the membranes in at least one of the other groups, introducing the feedstream into the first zone of one or more of the intermediate modules under conditions suitable for permeation, and thereby obtaining permeate effluents and non-permeate streams from the intermediate modules, collecting the permeate effluents from the second zones of one or more of the intermediate group modules, and distributing the permeates into the first zones of the first product group modules, under conditions suitable for permeation, and thereby separating therefrom non-permeate effluents and final permeate product streams, distributing the non-permeate streams from one or more of the intermediate modules into the first zone of the second product modules under conditions suitable for permeation, and thereby obtaining permeate effluents and non-permeate second product streams from the second product modules, collecting the permeate effluents from the second zones of the second product modules, and distributing the permeates into the first zones of one or more of the intermediate group modules, and distributing the non-permeate streams from the first product modules into the first zone of one or more of the intermediate modules under conditions suitable for permeation.
In yet another aspect, this invention provides a process using perm-selective membranes in groups for simultaneous recovery of a permeate product and a desired non-permeate product from a fluid mixture of compounds, which process comprises: providing a feedstream comprising a mixture of two or more organic compounds, providing apparatus comprising a plurality of membrane modules disposed in a first product group and a second product group, each module comprising first and second zones separated by a solid perm-selective membrane which under a suitable differential of a driving force exhibits a permeability of at least 1 Barrer for one of the compounds of the feedstock, each first zone having at least one inlet and outlet for flow of fluid in contact with the membrane, and contiguous with the opposite side thereof a second zone having at least one outlet for flow of permeate, introducing the feedstream into the first zone of the first product group of modules under conditions suitable for permeation, and thereby obtaining non-permeate effluents and final permeate product streams from the first product modules, collecting the non-permeate effluents from the second zones of the first product group modules, and distributing the non-permeate streams into the first zone of the second product modules under conditions suitable for permeation, and thereby obtaining permeate effluents and non-permeate second product streams from the second product modules, and collecting the permeate effluents from the second zones of the second product group of modules, and distributing the permeates into the first zones of the first product group modules.
For a more complete understanding of the present invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawing and described below by way of examples of the invention.